Effect of sintering on the optical properties of SiO2 colloidal crystal multilayers

High-quality SiO2 colloidal crystal multilayers were fabricated from ethanol solutions by the vertical deposition method and the effect of sintering on the optical properties of the samples was investigated. Optical properties,which are determined by the photonic band structure, weres tudied by means of light transmission and reflection measurements. The morphology of the samples was characterized by scanning electron microscopy (SEM). SEM images illustrate the ordered close package of the spherical colloids in planes parallel to the substrate surface. In addition, the sampie is crackless as a result of an appropriate drying rate. It is shown that with the increase of the sintering final temperature, though the depth and the width of the peak of Bragg diffraction of the sample vary vastly, the peak produces few blue shifts. Optical measurement results were compared favorably to the microstructural properties of the colloidal crystal multilayers.     

Properties and Morphology of TiN Films Deposited by Atomic Layer Deposition

In this study,TiN films were deposited on SiO2 substrates by Atomic Layer Deposition(ALD) using TiCl4and NH3 as precursors. Properties and morphology of the TiN films were characterized by different methods.Using Grazing Incidence X-Ray Diffraction(GIXRD),TiN films demonstrated polycrystalline structure with(111)preferred orientation. Film thickness was measured by Spectroscopic Ellipsometry(SE) and a stable growth rate of 0.0178 nm/cycle was reached after 500 deposition cycles,which was consistent with the essence of ALD as a surface-saturated self-limiting reaction. Film resistivity measured by a four-point probe continuously decreased with increasing deposition cycles until it reached the minimum value of 300μΩ cm at 5000 deposition cycles with a thickness of 87.04 nm. The surface roughness and morphology of the TiN films at different deposition cycles ranging from 50 to 400 were analyzed by Atomic Force Microscopy(AFM). The AFM results indicated that the initial film growth follows the Stranski-Krastanov mode.     

Novel trichromatic phosphor Co-doped with Eu, Tb in SiO2 gel matrix

The Eu, Tb co-doped SiO2 matrix tricolor fluorescence system was prepared by sol-gel technique. Red emission at 618 nm, green emission at 543 nm and blue emission at 350-500 nm were observed in the PL spectra of the sample, indicating that Eu^3＋, Eu^2＋ and Tb^3＋ ions coexisted in the matrix. In the co-doped sample, the blue emission of Eu^2＋ was much stronger than that of the sample single doped with Eu, which implied that the electron transfer between Eu^3＋ and Tb^3＋ maybe happened in the SiO2 matrix. The influences of the annealing temperature and Tb concentration on the PL spectra of the samples were investigated. The optimal doped concentration of Tb was determined to be 0.2% and the optimal annealing temperature 850℃. Annealed at 600℃, Tb^3＋ had a sensitizing effect on Eu^3＋ in the SiO2 matrix, and the emission intensity of Eu^3＋ in the Eu, Tb co-doped sample was more than four times that of the single doped sample, which could be attributed to the energy transfer from Tb^3＋ to Eu^3＋.     

Tricolor white emitting phosphor co-doped with Eu,Dy in SiO_2 matrix

A Eu, Dy co-doped SiO2 matrix, white emitting phosphor was prepared by the sol-gel technique. Strong red, green and blue emissions located at 618 nm, 573 nm and 400-550 nm were observed under UV laser excitation at room temperature. Such techniques as FT-IR and TGA-DSC were used to measure the microstructure of the luminescent material. The influence of the preparation techniques on the luminescence property of the Eu, Dy co-doped SiO2 matrix, such as anneal temperature, anneal time, dried atmosphere and the components of the matrix, was systematically studied, and the luminescence mechanism was interpreted. The red emission is the strongest when annealed at 750 ℃ . However, blue emission appears when annealed at 700 ℃ and is the intensest at 900℃ . For the samples dried in vacuum, Eu3 is more easily deoxidized to Eu2 at lower temperatures, because the samples dried in the air compared with that dried in vacuum need higher temperature to form network structures. Only the SA and SAB matrix annealed at 850 ℃ had blue emission in the four matrices (SA, SAB, SB, S) xerogel and the emission in the SAB matrix was stronger than that in the SA matrix. This may be due to the eutectic phase formed by the oxide boron, alkaline oxide and alumina in the SAB matrix, which constructs network structures and stabilizes the emission center and enhances the blue emission.     

Perpendicular magnetic anisotropy of Co85Cr50/Pt multilayers

The CoCr/Pt bilayers and (CoCr/Pt)₂₀ multilayers with Pt underlayer were prepared by DC magnetron sputtering. The effects of prepared condition on perpendicular magnetic anisotropy were investigated. The results show that the thickness of Pt underlayer has a great effect on the microstructure and perpendicular magnetic anisotropy of CoCr/Pt bilayers and (CoCr/Pt)₂₀ multilayers.When the thickness of Pt underlayer increases, Pt(111) and CoCr(002) peaks of both CoCr/Pt bilayers and (CoCr/Pt)₂₀ multilayers increase and the bilayer periodicity of the multilayers is improved. The effective magnetic anisotropy of (CoCr/Pt)₂₀ multilayers with Pt underlayer was much larger than that of CoCr/Pt bilayers. The (CoCr/Pt)₂₀ multilayers has a stronger perpendicular magnetic anisotropy than that of CoCr/Pt bilayers. This is ascribed to the interface magnetic anisotropy of the multilayers.     

A novel water-soluble anionic conjugated copolymer containing poly（p-phenylene vinylene） segments： Copolymer synthesis and multilayer construction by assembling poly（diallyl dimethyl ammonium chloride）

This paper reports the synthesis of a water soluble conjugated polymer poly（p-phenylene vinyleneco-sodium methacrylate） （ws-P（PV-co-SMA）） and the multilayer of the derived copolymer assembling poly（diallyl dimethyl ammanium chloride） （PDDA）. The self-assembling process of the multilayer was monitored by UV-vis absorption spectroscopy, and the data indicated a linear increase in film thickness with a number of ws-P（PV-co-SMA）/PDDA bilayers. The alternative deposition of ws-P （PV-co-SMA） and PDDA allowed the insertion of a non-conjugated layer between the conjugated layers, thus the migration of the photogenerated polarons was effectively confined in the isolated ws-P （PV-co-SMA） chains. Consequently, the photoluminescence quantum yield reached 0.68, 30 times higher than that of pure poly（p-phenylen vinylene）. The distinct electronic interactions between conjugated segments were confirmed by comparative analyses of the excitation spectra and time-resolved photoluminescence spectra of ws-P（PV-co-SMA） solid film and the assembled multilayers. The confinement effect of the PDDA layer on the photogenerated carriers was verified by the surface photovoltage spectroscopic measurement on both ws-P（PV-co-SMA） solid film and self-assembled multilayers.     

Tricolor white emitting phosphor co-doped with Eu, Dy in SiO2 matrix

A Eu, Dy co-doped SiO2 matrix, white emitting phosphor was prepared by the sol-gel technique. Strong red, green and blue emissions located at 618 nm, 573 nm and 400-550 nm were observed under UV laser excitation at room temperature. Such techniques as FT-IR and TGA-DSC were used to measure the microstructure of the luminescent material. The influence of the preparation techniques on the luminescence property of the Eu, Dy co-doped SiO2 matrix, such as anneal temperature, anneal time, dried atmosphere and the components of the matrix, was systematically studied, and the luminescence mechanism was interpreted. The red emission is the strongest when annealed at 750℃. However, blue emission appears when annealed at 700℃ and is the intensest at 900℃. For the samples dried in vacuum, Eu^3＋ is more easily deoxidized to Eu^2＋ at lower temperatures, because the samples dried in the air compared with that dried in vacuum need higher temperature to form network structures. Only the SA and SAB matrix annealed at 850℃ had blue emission in the four matrices （SA, SAB, SB, S） xerogel and the emission in the SAB matrix was stronger than that in the SA matrix. This may be due to the eutectic phase formed by the oxide boron, alkaline oxide and alumina in the SAB matrix, which constructs network structures and stabilizes the emission center and enhances the blue emission.     

Influence of deposition time on the morphology and optical properties of SiO<Subscript>2</Subscript>-ZnO composite photonic crystals

SiO2 photonic crystal were successfully prepared by vertical deposition and then used as a template to fabricate SiO2-ZnO composite photonic crystals on ITO substrates by electrodeposition and subsequent calcination. A number of different deposition times were used. The morphologies of the silica opals and SiO2-ZnO composite photonic crystals were investigated by scanning electron microscopy. It was found that ZnO particles grew randomly on the surfaces of the silica spheres when the deposition time was short. As the deposition time was increased, the ZnO particles grew evenly on the surfaces of the silica spheres so that the interstitial space of the silica template was filled with ZnO particles. Reflectance spectra of the SiO2-ZnO composite crystals revealed that all of the fabricated photonic crystals exhibit a photonic band gap in the normal direction.     

Microstructure and magnetic properties of FePt/MgO multilayers deposited by RF magnetron sputtering

FePt (50 nm) and [FePt(a nm)/MgO(b nm)₅/glass (a=1, 2, 3; b=1, 2, 3) films were prepared by radio frequency (RF) magnetron sputtering technique, and then were annealed at 600℃ for 30 min. The effect of MgO layer thickness on the structures and magnetic properties of the FePt/MgO multilayers was investigated. The coercivities and inter-grain interactions of the FePt/MgO films were decreased, yet the degree of (001) texturing drastically increased with the increase in MgO layer thickness when the FePt layer thickness was fixed. Thus, the FePt/MgO films with appropriate coercivities, high perpendicular anisotropy, and weak intergrain interactions were obtained by controlling the MgO layer thickness. Overall, these results indicate that the FePt/MgO nanostructured films are promising candidates for future high-density perpendicular recording media.     

Preparation of graphene and TiO2 layer by layer composite with highly photocatalytic efficiency

A process for fabricating graphene and TiO2 layer by layer composite was introduced to improve the photocatalytic activity by controlling the layers, thickness and the mass ratio between graphene and TiO2. The graphene oxide (GO) was synthesized from natural graphite pow der by the modified Hummers met hod. Large-area uniform GO and TiO2 thin films were made by a spin-coating process in turn. After exposure of the TiO2/GO multilayer film to UV light irradiation which allows the reduction of GO to graphene, a novel photocatalyt ic structure as graphene and TiO2 layer by layer composite was synthesized. The cross-sectional SEM image showed that a clear layer by layer microstructure with a single layer thickness of graphene or TiO2 was in the range of about 50 nm. The total thickness of the film was around 5 μm which was varied according to the layer number of spin coating process. Raman spectra revealed th at significant structural changes occurred through UV light irradiation. Photodegrada tion for methylene blue (MB) exhibited that the layer by layer com posite is of higher photocatalytic activity than the pure TiO2 layer.     

快速热退火对a-Si:H/SiO2多层膜光致发光的影响

采用在等离子体增强化学气相沉积(PFCVD)系统中沉积a-Si：H和原位等离子体逐层氧化的方法制备a-Si：H／SO2多层膜．用快速热退火对a-Si：H／SiO2多层膜进行处理，制备nc—Si/SiO2多层膜，研究了这种方法对a-Si：H／SiO2多层膜发光特性的影响．研究发现对a-Si：H／SiO2多层膜作快速热退火处理，可获得位于绿光和红光两个波段的发光峰．研究了不同退火条件下发光峰的变化．通过对样品的TEM、Raman散射谱和红外吸收谱的分析，探讨了a-Si：H／SiO2多层膜在不同退火温度下的光致发光机理．     

Si/SiO_2和Si/SiN_x/SiO_2超晶格的能带结构

利用Kronig-Penney模型从理论上计算了Si/SiO2和Si/SiNx/SiO2多层膜结构中量子阱的能带结构,进一步分析了各亚层薄膜厚度对能带结构和有效质量的影响.结果发现,适当减少亚层的厚度都能使得纳米Si薄膜的带隙发生明显宽化.在Si/SiO2超晶格中,Si量子阱层带隙能量随着Si层厚度的变化符合EPL(eV)=1.6+0.7/d2关系,与我们的计算结果十分吻合.在Si/SiNx/SiO2超晶格系统中,可以通过控制各亚层厚度,尤其是Si和SiNx层厚度,均能够有效地控制发光.     

退火温度对硅/氧化硅多层膜微结构的影响

采用等离子体增强化学气相淀积系统,应用原位氧化和原位掺杂技术制备出了非晶硅/二氧化硅多层膜结构。对多层膜结构进行不同温度下热退火后处理,通过傅里叶变化红外吸收光谱和拉曼散射光谱对其微结构的变化进行了表征。结果表明,原始淀积的多层膜结构中,存在大量的氢原子,以硅氢键和硅键合;随着退火温度从450℃升高到650℃,光谱中与硅氢键相关的信号逐渐减弱,说明氢原子不断解离;另一方面,硅氧键弯曲振动模式随着退火温度升高而增强;硅氧键的伸缩振动模式位置蓝移、强度增强,说明硅氧之间的配比随着退火温度升高不断接近化学配比;通过拉曼散射谱可以观测到非晶硅在高温下发生相变,形成纳米硅晶粒。     

Relationship between giant magnetoresistance of NiFe/Cu multilayers and their microstructures

The (111)-orientated NiFe/Cu multilayers were prepared by magnetron sputtering method. At room temperature, saturation magnetoresistances of NiFe/CU multilayers oscillate as a function of Cu spacer layer thickness. Two peak GMR values of 19.4%, 11.6% and 11.2%, 1% appear, respectively, at Cu sublayer thickness of t_Cu,= 1.0, 2.2 nm while the deposition pressures are 0.25 and 0.45 Pa. X-ray small-angle reflections and diffuse scattering at Cu K-edge (8.979 keV) by synchrotron radiation source were used to characterize the interfacial roughness. Diffraction anomalous fine-structure scattering (DAFS) was performed to investigate the local structure of NiFe and Cu sublayers. Results show that the deposition pressure has effect on interfacial roughness of the samples obviously, and the interfacial roughness also affects the GMR values of the samples strongly.     

SiO2/Ta interface reaction in magnetic multilayers and its influence on Ta buffer layers

Ta is often used as a buffer layer in magnetic multilayers. In this study, Ta/Ni81Fe19/Ta multilayers were deposited by magnetron sputtering on sing-crystal Si with a 300-nm-thick SiO2 film. The composition and chemical states at the interface region of SiO2/Ta were studied using the X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there is an "intermixing layer" at the SiO2/Ta interface due to a thermodynamically favorable reaction: 15 SiO2 + 37 Ta = 6 Ta2O5 + 5 Ta5Si3. Therefore, the Ta buffer layer thickness used to induce NiFe (111) texture increases.     

一种优越的钝化膜(a-Si:O:H)

本文报道了用等离子放电SiH_4+H_2+H_2O混合气体淀积氢化非晶硅氧合金膜,均匀、致密、耐腐蚀、半绝缘、电中性、富含氢,是较理想的半导体器件钝化膜。兼有SiO_2和a-Si:H的优点,而又克服了它们各自的缺点。用它钝化的平面晶体管放在盐水里几小时后,特性不变。     

Preparation of SiO<Subscript>2</Subscript> microspheres with sodium ions and self-assembly of photonic crystals

SiO2 microspheres were prepared via a novel co-precipitation process.The Na + ions were introduced by adding sodium chloride and metal sodium in solution systems for improving surface charge of the SiO2 microspheres.And then SiO2 photonic crystals were fabricated by the vertical deposition method.The electrical properties,micromorphology and optical properties were characterized by zeta potential instrument,scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy and Uv-Vis-Nir spectroph...     

The ultraviolet and blue luminescence properties of ZnO:Zn thin film

The ultraviolet (UV) and blue luminescence of Zn-rich zinc oxide thin film deposited by electron-beam evaporation have been investigated at room temperature (RT). We observed that the UV and blue electroluminescence (EL) emission band centered around 480 nm which is blue shifted in comparison with that of the ZnO thin film prepared by low pressure metal organic chemical vapor deposition (LP MOCVD). The UV emission is much stronger than blue emission in the photoluminescence (PL) spectra. The field-induced ionization of excited luminescent centers of ZnO:Zn thin film at high electric field and the difference between PL and EL are discussed. The experiments show that the ZnO:Zn thin film provides a hopeful new mechanism to obtain UV and blue emission.